Many types of invertible pumps are known, such as those described in U.S. Pat. No. 5,222,636, U.S. Pat. No. 4,775,079, U.S. Pat. No. 4,277,001, U.S. Pat. No. 5,353,969, U.S. Pat. No. 5,738,252, EP-A-0648545 and EP-A-1029597.
All pumps, whether invertible or non-invertible (i.e. usable with the pump only in the upright position) must enable air to escape from the compression chamber of each pump on priming (i.e. when the air present in the pump compression chamber must be expelled to the outside, to enable a vacuum to form in the chamber, with consequent drawing of liquid into the pump), and to enable external air to enter the container on which the pump is mounted when a vacuum forms in the container following liquid dispensing by the pump.
The problem of external air entry into the container is particularly delicate in the case of invertible pumps, because such pumps must be able to be used and operated without liquid leakage or escape when the pump is in the inverted position, i.e. surrounded by and immersed in liquid which collects in proximity to the container mouth when the pump is mounted; this means that air must be able to enter the container through passageways from which, however, the liquid must not flow or drip out.
The most effective system is that described in U.S. Pat. No. 5,353,969 in which between the outer surface of the end of the pump hollow body and the opposing inner surface of the ring cap which fixes the pump to the container mouth there is provided a long, thin spiral groove, of which one end is open to the pump exterior and the other end opens below the pump, i.e. in communication with the interior of the container on which the pump is mounted: the dimensioning of the spiral groove is critical, being such as to prevent liquid outflow through it (with consequent dripping from the pump when used in the inverted position) but to allow passage of the air drawn from the outside into the container when a vacuum is formed therein following liquid dispensing by the pump. However, this system presents numerous drawbacks, such as the considerable difficulty of moulding the various components of the pump, the structure of which is very complex, the possible outward dripping of liquid through the grooves when the pump is in its inverted position and is retained in that position without the pump being operated, and the possible escape through the grooves of vapour originating from the liquid enclosed in the container when the pump is in its upright position.